A monitoring apparatus is known from American patent specification U.S. Pat. No. 3,838,684. The monitoring apparatus comprises a pressure sensitive sensor, which during use abuts a part of a skin surface for measuring the heart rate. The pressure pulses obtained by the sensor are converted to an electrical pulse. Furthermore, a light source is provided which allows a user to count the light pulses representative of each heart beat during a 15 second interval to thereby determine visually what his heart rate is at any given time. The apparatus is compact and strapped about the wrist.
A disadvantage of the known monitoring apparatus is its unreliability, because in order to obtain good heart rate measurements, the pressure sensor is required to be located exactly on a position adjacent to a blood vessel from which the measurements are to be obtained. Therefore, the apparatus is not suitable for use by athletes who prefer to use the apparatus while running, jumping and/or moving in any other manner.